A motorcycle which has a water cooled engine of the conventional type is equipped with a radiator for cooling the engine by recirculating water. One kind of radiator comprises a pair of radiator units which are positioned at the front portion of the body of the motorcycle so as to introduce ram or on-coming air currents to the radiator for carrying out an effective heat exchange process.
In the prior art, radiators having various structures have been proposed wherein, for example, some of the motorcycles are equipped with separate radiator units, which are located just behind a head pipe and are positioned against a tank rail extending backwardly from the head pipe, and a down tube extends diagonally backwardly therefrom so as to permit installation of the radiator units in an upright fashion.
The radiator units of the character described above are generally arranged or connected in series or in parallel with each other for recirculating the cooling water.
In the case of the series arrangement of the radiator units, each of which comprises upper and lower tanks, a water tube connected to a water jacket is joined with the lower tank of one radiator unit. The upper tank of this radiator unit and the upper tank of the other radiator unit are interconnected by means of another water tube. A third water tube from the lower tank of the other radiator unit is led to a water pump so as to thereby circulate the cooling water through the radiator units.
In this series arrangement, however, a remarkable pressure drop within the radiator units, has been observed because the flow-path of the cooling water defined between the two radiator units is serially continuous and therefore the entire length of the flow-path is rendered quite long. Accordingly, the amount of cooling water circulating through or along the cooling water flow path is effectively restricted, resulting in a low efficiency of the heat exchange process.
On the other hand, in the case of the parallel arrangement of the radiator units, a water tube connected to a water jacket is branched into water tubes by means of a T-shaped joint and these water tubes are led and connected to the upper tanks of the respective radiator units. Water tubes connected to the lower tanks of the respective radiator units are combined into one tube, which is then led to the water pump so as to thereby circulate the cooling water through the radiator units. The upper tanks of both radiator units are also interconnected through means of an air ventilation hose.
The parallel arrangement of the radiator units may greatly resolve the pressure drop deficiency in comparison with the series arrangement of the radiator units, but the parallel arrangement requires a considerable number of water tubes as described above and the location of the T-shaped joint and the air ventilation hose renders the radiator structure relatively complex and, hence, involves increased cost.